The studies proposed will establish, for the neonatal submandibular gland of the rat, cell-type specific protein markers for the differentiation of the two secretory cell types. The proteins will be purified by preparative IEF on granulated gels, gel chromatography on Ultrogel AC-34, and native and/or SDS gel electrphoresis. Antibodies will be prepared in rabbits and purified on a Protein A-Sepharose CL 4B column. Purity of the antibodies will be established by quantitative immune precipitation of radioactively-labelled cellular proteins using insolubulized Protein A, and SDS gel electrophoresis to demonstrate identity of the precipitated antigens with the purified proteins. Abscence of the proteins from other organ types will be demonstrated by the quantitative immunoprecipitation procedure. Immunocytochemistry at the electron microscope level will test the hypothesis that one group of proteins is localized exclusively in one secretory cell type, under B - adrenergic regulation, that another protein is localized in the second cell type, under cholinergic regulation, and that a still different protein is found in both types of cells. For the neonatal sublingual gland, two proteins of the serous demilunes will be used as cell-specific markers based on the known positions of the protein bands on analytical IEF and SDS electrophoretic gels. Absence of the proteins from other cell types will be confirmed by the same procedure. Utrastructural analysis and the above procedures will be used to describe the process of cytodifferentiation in embryonic glands in organ cultures. Experimental tissue recombinations will be done to examine the factors involved in the specification of a submandibular or sublingual gland phenotype. We shall test the hypothesis that between 14 and 15 days postconception the submandibular phenotype becomes fixed and can be maintained by heterotypic mesenchymel and that the specification of phenotype depends on the age and degree of condensation of the mesenchyme, as well as the extent of its contact with epithelium, at the time that the rudiments form recognizable epithelial buds. We shall also test the ideas that the neural crest precursors to salivary mesenchyme acquire the capacity to elicit specific submandibular cytodifferentiation during their migration.